There is a continuing trend toward decreasing feature sizes and dimensions at submicron levels in fabricating semiconductor devices. The narrow widths/diameters and close spacing of features such as interconnecting lines and contact openings requires small features sizes produced by high-resolution photolithography. When defining lines with small widths or critical dimensions (CD) and close pitch distances, variations that occur in patterning such features become problematic due to the small size and closeness of features. One such variation is known as “line edge roughness” (LER), which is a horizontal deviation or measurement of unwanted edges and bumps on a boundary such as a line edge or sidewall of a patterned feature, making it appear ragged rather than smooth. In addition, a line is ideally straight such that the width is approximately identical for the entire length of the feature (e.g., a critical dimension 25 nm wide line). “Line width roughness” (LWR) is a deviation in the width or CD of a line feature due to a variation in peak-to-valley amplitude of a non-uniform line edge along its length.
Line defects such as LWR and LER occurring in patterned features can be caused, for example, by a corresponding defect within an overlying photoresist or hard mask pattern that is transferred into an underlying material layer or film during a subsequent etch. Line defects introduced during patterning becomes more pronounced as device features continue to shrink in size, impacting process control by causing variations in channel and line dimensions beyond accepted limits and/or improper overlay or placement control of features, which presents a significant adverse effect on device performance and function including problems of leakage and short channel effect control. For example, lines that have a width of 70 nm or less, a peak-to-valley LWR of 3 nm or more can alter the subsequently patterned feature beyond acceptable tolerances.
Attempts have been made to reduce line defects on oxide-based mask lines by eliminating undesirable curves and protrusions such as whiskers. Treatments involving a wet etch, such as an HF wet chemistry, etch oxide features isotropically (i.e., equally in vertical and horizontal directions) resulting in an overall trimming (thinning) of the feature without eliminating unwanted curves or straightening the lines. Other treatments that involve depositing material (e.g., polymer) to smooth out a line feature followed by a plasma etch back to resize the feature, also reduce the vertical height or thickness of the line, which is undesirable in a mask structure.
It would be useful to provide a method for eliminating line roughness defects in features that overcome these or other problems.